The invention concerns a horizontal drilling and milling machine of the type comprising a vertically movable headstock which carries a horizontally adjustable spindle sleeve. A counterweight is connected to the headstock by a pair of vertical chains.
In apparatus of the type wherein a spindle sleeve is run-out or extended from a headstock, there is a tendency for the front end of the spindle to deflect downwardly relative to the headstock and travel along a non-linear path. The deflection is an exponential function of the extent of run-out of the spindle sleeve and may assume, for example the pattern B or B' shown in FIG. 3. That is, the front end of the tool-carrying spindle sleeve traces, during the run-out of the spindle sleeve, a dislocation line, which results, for example, from the deformation of the vertical guide elements due to the shifting of the center of gravity caused by the displacement of the spindle sleeve, and the weight of the tool at the front end of the spindle sleeve.
Attempts to counteract such deflections to minimize the extent to which the front end of the spindle sleeve deviates from a desired zero deviation line (e.g., line N in FIG. 3) have included by the provision of a counterweight system connected to the headstock by means of chains. As the spindle sleeve is run-out the counterweight system is adjusted to shift the headstock counter to the displacement of the spindle sleeve and thereby reduce the extent to which the path of travel of the spindle sleeve deviates from the desired travel path.
A horizontal drilling and milling machine of this type is known from German OS No. 21 47 985. Therein, the position of the center of gravity of the counterweight is varied by the shortening or lengthening of at least one of the connecting chains between the headstock and the counterweight in or approximately in the horizontal direction. In this known machine there exists a strict linearity between the longitudinal movement of the spindle sleeve on the headstock and the shortening or lengthening of the one chain between the headstock and the counterweight in that end of the front chain connected with the headstock, i.e., the chain facing the front side of the headstock, is adjusted by means of a mechanical transfer system of shafts and conical gear wheels directly by the drive shaft or spindle of the spindle sleeve.
From German AS No. 27 42 642 there is further known a device for the weight balancing of an instrument part movable on an X-ray apparatus, wherein the balancing of the camera, the amplifier and the target device, suspended on a common supporting cable, is effected by means of a prestressed system of springs or a servomotor, controlled by a device measuring the strain of the common support cable, for example a strain gage.
From German AS No. 1 261 730 a weight equalizing device, in particular for the headstock of a drilling and milling machine, is known, wherein the headstock is horizontally displaceable in a vertically guided slide, and is connected by means of a cable with a vertically displaceable counterweight. The counterweight is guided on two rolls, arranged on a supporting beam pivoting around a vertical axle on the upper end of the machine frame. In case of a horizontal movement of the headstock in the vertically guided slide, the supporting beam performs, with the aid of a gear, a pivoting motion, whereby the headstock is caused to effect with one end of the cable a horizontal movement in one direction and the counterweight with the second cable end a similar movement in the opposite direction, so that the resultant of the forces of the headstock and of the counterweight is always passing through the axis of the pivoting beam.
Finally, from German AS No. 1 602 736 there is known a counterweight suspension for drilling and milling machines having a run-out spindle sleeve. Equalization of the differential strain in two tension ropes loaded with a counterweight and connected with their ends adjacent to the headstock with the ends of a beam varies the annular position of the headstock with respect to the horizontal in a vertical plane. The headstock is supported by a roll to be displaced simultaneously with the spindle sleeve relative to the beam by means of an adjusting gear.
The above-mentioned state of the art includes only devices wherein there is effected a linear adjustment of the deflection range of the moving element, i.e., the camera, target device, or drilling spindle or the headstock. That is, some of but not all of the deflection is compensated for by the linear adjustment effected by the prior art.
It is therefore an object of the invention to minimize or obviate problems of the type discussed above.
Another object is to more precisely compensate for the deviations of a moving spindle sleeve.
A further object of the invention is to comply with the exponential line of displacement of the spindle sleeve and respectively with the curve described by the front end of the spindle sleeve and its tool during longitudinal movement of the spindle sleeve, and to equalize the deviation of this line or curve from the zero line in the extension of the axis of the spindle sleeve. This condition is to be satisfied even in the case of the spindle sleeve being provided with different tools. The mechanism used in the process should be simple in design and easily handled.